The broad, long term objective of this project is the development of a noninvasive optical technique for imaging in vivo blood flow dynamics and tissue structure with high spatial resolution. Optical Doppler Tomography (ODT) combines Doppler velocimetry with optical coherence tomography (OCI) to measure blood flow velocity at discrete user-specified locations in highly scattering biological tissues. The exceptionally high resolution of ODT allows noninvasive imaging of both in vivo blood microcirculation and tissue structures surrounding the vessel. The rationale for using ODT to characterize the underlying microvasculature is that the technique is able to probe with high spatial resolution at discrete user-specified locations in biological tissues. Such localization is possible because the detected ODT interference fringe intensity gives accurate discrimination of the optical path length of Doppler shifted and backscattered light to within the source coherence length. Furthermore, in contrast to laser Doppler flowmetry, the overall ODT signal due to moving red blood cells (RBC) is almost entirely due to the Doppler shifted light. As a result, signal-to-noise ratios (SNR) are substantially higher. Inasmuch as tomographic images of blood flow and tissue structure can be obtained simultaneously from a single scan, ODT has decided advantages over existing methodologies. In preliminary studies conducted on in vitro and in vivo turbid samples and model vasculatures, respectively, the feasibility and potential application of ODT to characterize and image blood flow with high spatial resolution at discrete user-specified locations in highly scattering biological tissues was reported by the applicants to have been demonstrated. Further study appears warranted. The objective of the studies proposed herein is to extend these initial findings and was projected by the applicants to lead to the development of a new technology for the clinical management of patients in whom microvascular monitoring is essential.